(i) Field of the Invention
The present invention relates to a plating technique, particularly to a technique of providing a catalyst for electroless plating.
(ii) Description of the Related Art
Heretofore, to provide a catalyst as a pretreatment for giving electroless plating on a non-metal or a metal having no (or little) catalytic activity, there has been employed in most cases a method which comprises the steps of giving sensitivity by use of a tin-containing solution and then giving catalytic activity by use of a palladium-containing solution. In addition, a method of treating an object by use of one solution containing both palladium and tin has also been widely used. In any case, it can be said that substantially only palladium is a metal which is industrially used as a catalyst for electroless plating.
Such a method of providing a catalyst by palladium and tin has such problems as described below.                (1) A production cost increases as a result of an increase in the price of palladium.        (2) In a production process of, for example, a printed board, palladium adsorbed on the surface of a resin in providing a catalyst for electroless copper plating remains as a smut even after etching of a copper plated film, and subsequent electroless nickel plating is inconveniently deposited not only on a circuit pattern portion but also on the resin.        
It has already been researched to replace palladium with another inexpensive metal. Roughly, (1) a method using a colloidal solution of a metal such as silver, copper or nickel and (2) a method using a colloidal solution of a hydroxide or oxide of a metal such as nickel or copper have already been reported or applied for a patent and disclosed.
More specifically, as the above method (1) using a metal colloidal solution, the following methods are disclosed. Japanese Patent Application Laid-Open No. 6861/1994 discloses a silver colloidal solution having excellent storage stability and a preparation method thereof. Japanese Patent Application Laid-Open No. 195667/1998 discloses a catalyst solution containing at least one of palladium, platinum, gold, silver and copper salts, an inorganic acid and a water-soluble unsaturated organic compound. Japanese Patent Application Laid-Open No. 209878/1999 discloses use of a tertiary amine polymer or quaternary ammonium polymer as a colloid stabilizer in preparing a colloidal solution by reducing ruthenium, rhodium, nickel, palladium, platinum, silver and gold with a boron hydride compound, an amine borane compound, formalin, hydrazine and a hypophosphite. Japanese Patent Application Laid-Open No. 241170/1999 discloses a solution containing an iron, nickel or cobalt compound as well as a silver salt, an anion compound and a reducing agent. Japanese Patent Application Laid-Open No. 167647/2001 discloses use of a hydroxy acid salt having at least three —COOH and —OH groups in total, the number of —COOH groups being equal to or larger than the number of —OH groups, particularly use of a citrate, as a dispersant. Japanese Patent Application Laid-Open No. 32092/2001 discloses use of a noble metal salt of methanesulfonic acid as a noble metal colloid.
Such patents may contain descriptions about copper, nickel and other metals as metal components forming a colloid. However, from the viewpoint of practical performance, a metal colloid which may possibly be industrialized is limited to a silver colloid.
Meanwhile, as the above method (2) using a hydroxide colloidal solution, the following methods are disclosed.
Heretofore, Iwai et al. have reported the results of carrying out electroless copper plating by immersing objects to be plated in hydroxide colloidal solutions prepared by addition of alkali to solutions of NiSO4, NiCl2, CuSO4 and CuCl2 and then immersing the immersed objects in a KBH4 solution so as to reduce the colloids and provide catalytic activity, with reference to U.S. patents (U.S. Pat. Nos. 4,048,354, 4,131,699 and 4,180,600) (Masao Iwai, Hiroshi Majima, Yasuhiro Awakura, The Journal of the Metal Finishing Society of Japan, Vol. 38, No. 6, 1987). In this report, they have also studied colloids of lead, cobalt, cadmium, zinc, manganese and aluminium in addition to nickel and copper. In recent years, new attempts made based on the studies have been reported. Japanese Patent Application Laid-Open No. 209878/1999 discloses a method of stabilizing a metal hydroxide colloid. The publication introduces, as a preferred reducing agent for reducing the colloid, a mixture of one or more components selected from the group consisting of a boron hydride compound, an amine borane compound, formalin, hydrazine and a hypophosphite. Japanese Patent Application Laid-Open No. 82878/2000 discloses use of the above method for production of a buildup multilayer printed wiring board and introduces potassium borohydride as an example of a reducing agent. Tsuru et al. have reported a study to improve adhesion by reducing a metal hydroxide colloid adsorbed to the surface of an object to be plated in the same manner as described above by use of a sodium borohydride solution and then reducing the resulting colloid by use of a hypophosphorous acid solution (Yutaka Tsuru, Michiyuki Kume, Yashichi Oyagi, Proceedings of the 15th JIEP Annual Meeting, page 25, 2001). Further, Tsuru et al. have also reported that when carbon and zinc are deposited by vacuum deposition after adsorption of the metal hydroxide colloid and the resulting colloid is immersed in acid, the colloid is reduced at the time of dissolution of zinc, whereby a catalyst for electroless plating can be provided (Yutaka Tsuru, Rie Odajima, Michiyuki Kume, Yashichi Oyagi, Summary of the 103th SFSJ Meeting, page 150, 2001). Yanagimoto et al. have obtained a thin copper film by coating a solution having superfine copper oxide particles dispersed in ethanol on an AlN board by spin coating, firing the coated board at 600 to 1,000° C., reducing the copper oxide in a hydrogen atmosphere and then carrying out electroless copper plating (Hiroshi Yanagimoto, Kensuke Akamatsu, Naruhito Ideki, Kazuo Goto, Summary of the 68th ECSJ Meeting, page 410, 1S07, 2001).
Despite these many studies, methods using metals other than palladium are not yet used industrially because they provide lower catalytic activity than the method using palladium and a method for preparing a stable solution is not yet established.
Patent Document 1
Japanese Patent Application Laid-Open No. 6861/1994
Patent Document 2
Japanese Patent Application Laid-Open No. 195667/1998
Patent Document 3
Japanese Patent Application Laid-Open No. 209878/1999
Patent Document 4
Japanese Patent Application Laid-Open No. 241170/1999
Patent Document 5
Japanese Patent Application Laid-Open No. 167647/2001
Patent Document 6
Japanese Patent Application Laid-Open No. 32092/2001
Patent Document 7
U.S. Pat. No. 4,048,354
Patent Document 8
U.S. Pat. No. 4,131,699
Patent Document 9
U.S. Pat. No. 4,180,600
Patent Document 10
Japanese Patent Application Laid-Open No. 82878/2000
Non-Patent Document 1
Masao Iwai, Hiroshi Majima, Yasuhiro Awakura, The Journal of the Metal Finishing Society of Japan, Vol. 38, No. 6, 1987
Non-Patent Document 2
Yutaka Tsuru, Michiyuki Kume, Yashichi Oyagi, Proceedings of the 15th JIEP Annual Meeting, 2001, page 25
Non-Patent Document 3
Yutaka Tsuru, Rie Odajima, Michiyuki Kume, Yashichi Oyagi, Summary of the 103th SFSJ Meeting, 2001, page 150
Non-Patent Document 4
Hiroshi Yanagimoto, Kensuke Akamatsu, Naruhito Ideki, Kazuo Goto, Summary of the 68th ECSJ Meeting, 1S07, 2001, page 410